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<head><meta charset="utf-8"><title>reverting universes · wg-traits · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/index.html">wg-traits</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html">reverting universes</a></h3>

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<a name="158651941"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158651941" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158651941">(Feb 15 2019 at 21:41)</a>:</h4>
<p>So if we wanted to "revert" universes, how would we go about it? It's a bit tricky.</p>
<p>I could of course just try to straight-up <code>git revert</code> and deal with the conflicts. Probably most of it comes from <span class="user-mention" data-user-id="116113">@lqd</span>'s changes to improve diagnostics. </p>
<p>But what if we tried to reproduce the same semantics we had before, but in the new system. One challenge is that this semantics was a bit inconsistent and buggy (e.g., we had to move NLL to universes to deal with that).</p>
<p>Certainly one thing we could do is to just layer the "leak check" back on for now. Basicallly, wherever we instantiate placeholders now, we would keep doing so -- but we would remember the universe and we would do a "leak check" that checks to see if any placeholders in this universe are related to some variable that is an outer universe. (We could even do this bidirectionally, to be as buggy as before.)</p>
<p>That's...actually probably fairly easy to do.</p>



<a name="158652157"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652157" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652157">(Feb 15 2019 at 21:44)</a>:</h4>
<p>interesting, is that somewhat of a backup plan or a likely direction ?</p>



<a name="158652286"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652286" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652286">(Feb 15 2019 at 21:46)</a>:</h4>
<p><span class="user-mention" data-user-id="116113">@lqd</span> I see it just as a "buy some time" plan</p>



<a name="158652300"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652300" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652300">(Feb 15 2019 at 21:46)</a>:</h4>
<p>I don't think it's something we'd really want to do</p>



<a name="158652319"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652319" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652319">(Feb 15 2019 at 21:47)</a>:</h4>
<p>although it could be used in specific places as a kind of efficiency change</p>



<a name="158652335"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652335" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652335">(Feb 15 2019 at 21:47)</a>:</h4>
<p>it's coming on 5pm here so i'm probably not going to pursue this much tonight</p>



<a name="158652434"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652434" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652434">(Feb 15 2019 at 21:48)</a>:</h4>
<p><span class="user-mention" data-user-id="116113">@lqd</span> to elaborate a bit more, it's not that I think the new system is <em>wrong</em>, but there may be some subtleties, and there is some value in trying to preserve the existing behavior while we talk things out more fully</p>



<a name="158652449"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652449" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652449">(Feb 15 2019 at 21:48)</a>:</h4>
<p>(specifically, I think it may require changes in <em>other</em> parts of the lang that have been kind of "papered over")</p>



<a name="158652452"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652452" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652452">(Feb 15 2019 at 21:48)</a>:</h4>
<p>it's a least nice to have this possibility in case we need it !</p>



<a name="158652651"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158652651" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158652651">(Feb 15 2019 at 21:51)</a>:</h4>
<p>Yeah, I'm looking a <em>bit</em> into what it would take</p>



<a name="158905031"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905031" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905031">(Feb 19 2019 at 18:25)</a>:</h4>
<p>OK I started looking at this a bit</p>



<a name="158905057"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905057" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905057">(Feb 19 2019 at 18:25)</a>:</h4>
<p>I didn't get too far but I think it would work</p>



<a name="158905168"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905168" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905168">(Feb 19 2019 at 18:26)</a>:</h4>
<p>I'm debating whether this is something that e.g. might be a good fit for <span class="user-mention" data-user-id="116010">@Aaron Turon</span>, or whether to try and tackle it myself. Could be something to hand off a bit, I'm concerned about time.</p>



<a name="158905203"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905203" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905203">(Feb 19 2019 at 18:27)</a>:</h4>
<p>i'm certainly game to try!</p>



<a name="158905280"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905280" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905280">(Feb 19 2019 at 18:27)</a>:</h4>
<p>how confident are we that the leak check is the only difference?</p>



<a name="158905309"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905309" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905309">(Feb 19 2019 at 18:28)</a>:</h4>
<p>lemme put that differently</p>



<a name="158905372"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905372" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905372">(Feb 19 2019 at 18:28)</a>:</h4>
<p>one worry, given that we're close to release, is that we try to "patch" the universes code to not change the behavior, but we don't get it totally right</p>



<a name="158905381"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158905381" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158905381">(Feb 19 2019 at 18:28)</a>:</h4>
<p>maybe a crater run of the patch could give us some confidence?</p>



<a name="158906024"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906024" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906024">(Feb 19 2019 at 18:34)</a>:</h4>
<p>that would help, although the existing PR didn't show any problems in crater</p>



<a name="158906041"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906041" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906041">(Feb 19 2019 at 18:34)</a>:</h4>
<p>that said, I'm pretty confident that the leak check is the only difference</p>



<a name="158906060"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906060" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906060">(Feb 19 2019 at 18:34)</a>:</h4>
<p>I mean that is literally the thing that was replaced</p>



<a name="158906077"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906077" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906077">(Feb 19 2019 at 18:34)</a>:</h4>
<p>but really the question is, if we try to "restore" the old behavior, are we going to wind up "preserving" it</p>



<a name="158906095"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906095" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906095">(Feb 19 2019 at 18:35)</a>:</h4>
<p>it's hard to say</p>



<a name="158906147"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906147" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906147">(Feb 19 2019 at 18:35)</a>:</h4>
<p>hmm. so next release is feb 28</p>



<a name="158906152"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906152" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906152">(Feb 19 2019 at 18:35)</a>:</h4>
<p>certainly the sooner we can land, the better</p>



<a name="158906166"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906166" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906166">(Feb 19 2019 at 18:35)</a>:</h4>
<p>this suggests it's worth frontloading some effort to this afternoon</p>



<a name="158906174"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906174" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906174">(Feb 19 2019 at 18:36)</a>:</h4>
<p>and/or now-ish</p>



<a name="158906447"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906447" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906447">(Feb 19 2019 at 18:38)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> OK, that is a pretty tight deadline. i'm happy to start poking at it but would certainly need help. if you think it's easiest for you to just knock it out, totally fine</p>



<a name="158906471"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906471" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906471">(Feb 19 2019 at 18:38)</a>:</h4>
<p>well, so, a thing we could do is to do some "pair prog" time on it</p>



<a name="158906480"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906480" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906480">(Feb 19 2019 at 18:39)</a>:</h4>
<p>with the goal of being able to "hand off"</p>



<a name="158906507"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906507" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906507">(Feb 19 2019 at 18:39)</a>:</h4>
<p>i.e., I have some time today, but I feel like time may be tight over next few days</p>



<a name="158906528"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906528" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906528">(Feb 19 2019 at 18:39)</a>:</h4>
<p>sure thing</p>



<a name="158906557"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906557" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906557">(Feb 19 2019 at 18:39)</a>:</h4>
<p>I plan to start poking at this at 3pm my time</p>



<a name="158906738"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906738" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906738">(Feb 19 2019 at 18:41)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> sgtm, i'll be ready to pair</p>



<a name="158906805"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158906805" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158906805">(Feb 19 2019 at 18:42)</a>:</h4>
<p>we could  do zoom + record, for other WG-traits folks</p>



<a name="158907715"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158907715" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158907715">(Feb 19 2019 at 18:50)</a>:</h4>
<p>sure</p>



<a name="158907727"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158907727" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158907727">(Feb 19 2019 at 18:50)</a>:</h4>
<p>plus, others find it helpful to be able to review</p>



<a name="158907733"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158907733" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158907733">(Feb 19 2019 at 18:50)</a>:</h4>
<p>particularly if I'm driving and making emacs jump all over the place :P</p>



<a name="158907747"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158907747" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158907747">(Feb 19 2019 at 18:51)</a>:</h4>
<p>hah <span aria-label="+1" class="emoji emoji-1f44d" role="img" title="+1">:+1:</span></p>



<a name="158914885"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158914885" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158914885">(Feb 19 2019 at 20:10)</a>:</h4>
<p><span class="user-mention" data-user-id="116010">@Aaron Turon</span> ok I'm planning to start on this soon</p>



<a name="158914894"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158914894" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158914894">(Feb 19 2019 at 20:10)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> ready when you are!</p>



<a name="158915109"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158915109" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158915109">(Feb 19 2019 at 20:13)</a>:</h4>
<p>ok, few more minutes</p>



<a name="158915234"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158915234" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158915234">(Feb 19 2019 at 20:14)</a>:</h4>
<p><span class="user-mention" data-user-id="116010">@Aaron Turon</span> (and anyone else who wants), connect to <a href="https://zoom.us/j/181515793" target="_blank" title="https://zoom.us/j/181515793">https://zoom.us/j/181515793</a></p>



<a name="158918817"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158918817" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> tmandry <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158918817">(Feb 19 2019 at 21:04)</a>:</h4>
<p>Was in the air for this meeting, but happy to review when it comes out on video</p>



<a name="158920636"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158920636" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158920636">(Feb 19 2019 at 21:29)</a>:</h4>
<p>so we didn't wind up doing any coding</p>



<a name="158920648"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158920648" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158920648">(Feb 19 2019 at 21:29)</a>:</h4>
<p>but instead spent a while talking about the implications of subtyping and soundness</p>



<a name="158920720"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158920720" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158920720">(Feb 19 2019 at 21:30)</a>:</h4>
<p>I convinced myself that the current coherence rules are definitely incorrect, in that they permit overlapping types</p>



<a name="158920742"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158920742" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158920742">(Feb 19 2019 at 21:30)</a>:</h4>
<p>we also creeped each other out with some of the implications but failed so far to uncover a weaponized problem</p>



<a name="158920764"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158920764" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158920764">(Feb 19 2019 at 21:31)</a>:</h4>
<p>and I feel mildly convinced that -- if such a problem exists -- it's because of <em>other</em> rules that need to be adjusted =)</p>



<a name="158924008"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924008" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924008">(Feb 19 2019 at 22:12)</a>:</h4>
<p>so the question <em>now</em> is</p>



<a name="158924074"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924074" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924074">(Feb 19 2019 at 22:13)</a>:</h4>
<p>do I try to push through the "bring back the leak check for now" change?</p>



<a name="158924132"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924132" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924132">(Feb 19 2019 at 22:14)</a>:</h4>
<p>and, if not, maybe what other things...do we have to do</p>



<a name="158924183"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924183" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924183">(Feb 19 2019 at 22:14)</a>:</h4>
<p>thinking on it a bit, I realize that e.g. <a href="https://github.com/rust-lang/rust/issues/57639" target="_blank" title="https://github.com/rust-lang/rust/issues/57639">#57639</a> kind of amounts to doing some limited form of the leak check</p>



<a name="158924246"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924246" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924246">(Feb 19 2019 at 22:15)</a>:</h4>
<p>OK -- i personally don't have quite enough of the pieces to  be able to connect the dots</p>



<a name="158924325"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924325" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924325">(Feb 19 2019 at 22:16)</a>:</h4>
<p>it does seem like getting the leak check re-instated is the obviously conservative thing to do</p>



<a name="158924335"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924335" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924335">(Feb 19 2019 at 22:16)</a>:</h4>
<p>and it's starting to feel like really figuring out what we want here may take some time</p>



<a name="158924343"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924343" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924343">(Feb 19 2019 at 22:16)</a>:</h4>
<p>whereas, IIUC, reinstating the leak check shouldn't be too hard</p>



<a name="158924370"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924370" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924370">(Feb 19 2019 at 22:16)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> ^</p>



<a name="158924509"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924509" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924509">(Feb 19 2019 at 22:18)</a>:</h4>
<p>Yeah, that is roughly my feeling. I think it remains true that the universe check is just "more correct", but that doesn't mean that it's right to institute it <em>now</em></p>



<a name="158924523"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924523" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924523">(Feb 19 2019 at 22:18)</a>:</h4>
<p>i.e., we might want to put through other mitigating changes first</p>



<a name="158924540"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924540" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924540">(Feb 19 2019 at 22:18)</a>:</h4>
<p>yeah</p>



<a name="158924615"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924615" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924615">(Feb 19 2019 at 22:19)</a>:</h4>
<p>in retrospect, I shouldn't have pushed through the full check, I always meant to reimplement the leak check in terms of universes anyway, but the clean crater run tempted me, and I confess I didn't anticipate all of these other interactions</p>



<a name="158924727"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924727" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924727">(Feb 19 2019 at 22:20)</a>:</h4>
<p>i mean the universe-based check seems a lot more elegant, i can understand the desire</p>



<a name="158924754"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924754" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924754">(Feb 19 2019 at 22:20)</a>:</h4>
<p>mostly I meant to take an "in between" step</p>



<a name="158924759"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924759" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924759">(Feb 19 2019 at 22:20)</a>:</h4>
<p>yeah</p>



<a name="158924883"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924883" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924883">(Feb 19 2019 at 22:22)</a>:</h4>
<p>FWIW you technically have until ~Sunday night to land whatever it is; I will note that the queue has been quite slow so we'll want to have it up at least 9-12 hours before we expect it to land</p>



<a name="158924917"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924917" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924917">(Feb 19 2019 at 22:22)</a>:</h4>
<p>(and if necessary there is technically some wiggle room on the release side -- we could slip by a day without affecting Thursday release)</p>



<a name="158924934"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924934" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924934">(Feb 19 2019 at 22:23)</a>:</h4>
<p>Yeah, I'm just a bit nervous about things here</p>



<a name="158924943"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924943" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924943">(Feb 19 2019 at 22:23)</a>:</h4>
<p>how is the crater queue etc?</p>



<a name="158924948"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924948" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924948">(Feb 19 2019 at 22:23)</a>:</h4>
<p>for an e.g. check-only crater run?</p>



<a name="158924956"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924956" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924956">(Feb 19 2019 at 22:23)</a>:</h4>
<p>is that still reasonably quick</p>



<a name="158924967"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924967" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924967">(Feb 19 2019 at 22:23)</a>:</h4>
<blockquote>
<p>Yeah, I'm just a bit nervous about things here</p>
</blockquote>
<p>that is, I don't want to introduce ICEs etc</p>



<a name="158924968"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158924968" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158924968">(Feb 19 2019 at 22:23)</a>:</h4>
<p>Crater queue is currently empty -- I believe check only is approx. 36 hours (<a href="https://crater.rust-lang.org/" target="_blank" title="https://crater.rust-lang.org/">https://crater.rust-lang.org/</a>)</p>



<a name="158925052"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158925052" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158925052">(Feb 19 2019 at 22:24)</a>:</h4>
<p>But <span class="user-mention" data-user-id="121055">@Pietro Albini</span> can give more accurate timeline on how long crater takes probably</p>



<a name="158925083"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158925083" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Pietro Albini <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158925083">(Feb 19 2019 at 22:24)</a>:</h4>
<p>check-only is ~1.5 days</p>



<a name="158925091"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158925091" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158925091">(Feb 19 2019 at 22:24)</a>:</h4>
<p>OK</p>



<a name="158925101"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158925101" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158925101">(Feb 19 2019 at 22:24)</a>:</h4>
<p>I'll see if I can pull together a PR tonight/tomorrow morning</p>



<a name="158925110"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158925110" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158925110">(Feb 19 2019 at 22:24)</a>:</h4>
<p>seems plausible</p>



<a name="158925134"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158925134" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158925134">(Feb 19 2019 at 22:25)</a>:</h4>
<p>gotta go fix dinner now :)</p>



<a name="158925147"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158925147" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158925147">(Feb 19 2019 at 22:25)</a>:</h4>
<p>ok, thanks <span class="user-mention" data-user-id="116009">@nikomatsakis</span></p>



<a name="158926674"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158926674" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158926674">(Feb 19 2019 at 22:45)</a>:</h4>
<p>I'm putting together some notes <a href="https://paper.dropbox.com/doc/The-move-to-universes-in-rustc--AX4MgFY_qFStpLwq1HT7ncjNAg-aODQm3DvOKf4Bwlnk6QpO" target="_blank" title="https://paper.dropbox.com/doc/The-move-to-universes-in-rustc--AX4MgFY_qFStpLwq1HT7ncjNAg-aODQm3DvOKf4Bwlnk6QpO">here</a> for the move to universes in general</p>



<a name="158928425"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158928425" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158928425">(Feb 19 2019 at 23:08)</a>:</h4>
<p>cool</p>



<a name="158967672"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158967672" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158967672">(Feb 20 2019 at 11:44)</a>:</h4>
<p>PR implementing the revert strategy I floated here: <a href="https://github.com/rust-lang/rust/pull/58592" target="_blank" title="https://github.com/rust-lang/rust/pull/58592">https://github.com/rust-lang/rust/pull/58592</a></p>



<a name="158967676"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158967676" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158967676">(Feb 20 2019 at 11:45)</a>:</h4>
<p>Still doing some test runs locally</p>



<a name="158987065"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158987065" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158987065">(Feb 20 2019 at 15:51)</a>:</h4>
<p>Did my best to summarize the universe situation here: <a href="https://github.com/rust-lang/rust/issues/56105#issuecomment-465634661" target="_blank" title="https://github.com/rust-lang/rust/issues/56105#issuecomment-465634661">https://github.com/rust-lang/rust/issues/56105#issuecomment-465634661</a></p>



<a name="158989487"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158989487" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158989487">(Feb 20 2019 at 16:15)</a>:</h4>
<p>(in case you haven't noticed, the leak-check revival PR <a href="https://github.com/rust-lang/rust/issues/58592" target="_blank" title="https://github.com/rust-lang/rust/issues/58592">#58592</a> has been blocked from running the CI tests by the merciless tidy)</p>



<a name="158993377"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158993377" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158993377">(Feb 20 2019 at 17:07)</a>:</h4>
<p>OK, i'm starting to review this morning</p>



<a name="158994287"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158994287" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158994287">(Feb 20 2019 at 17:20)</a>:</h4>
<p><span class="user-mention" data-user-id="116113">@lqd</span> thanks -- I'm currently getting the tests to pass</p>



<a name="158994297"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158994297" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158994297">(Feb 20 2019 at 17:20)</a>:</h4>
<p>and will then address the merciless tidy</p>



<a name="158996315"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158996315" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158996315">(Feb 20 2019 at 17:45)</a>:</h4>
<p>done reviewing</p>



<a name="158997278"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158997278" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158997278">(Feb 20 2019 at 17:56)</a>:</h4>
<p><span class="user-mention" data-user-id="116010">@Aaron Turon</span> I'll take a look -- so I also went over all the tests. Most of the new output made sense to me but for one example that surprised me.</p>



<a name="158997373"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158997373" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158997373">(Feb 20 2019 at 17:57)</a>:</h4>
<p>This example used to error out but now does not:</p>
<div class="codehilite"><pre><span></span><span class="k">fn</span> <span class="nf">foo</span><span class="p">(</span><span class="w"></span>
<span class="w">    </span><span class="n">x</span>: <span class="kp">&amp;</span><span class="nc">for</span><span class="o">&lt;</span><span class="na">&#39;a</span><span class="p">,</span><span class="w"> </span><span class="na">&#39;b</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Foo</span><span class="o">&lt;&amp;</span><span class="na">&#39;a</span><span class="w"> </span><span class="kt">u8</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="na">&#39;b</span><span class="w"> </span><span class="kt">u8</span><span class="o">&gt;</span><span class="p">,</span><span class="w"></span>
<span class="w">    </span><span class="n">y</span>: <span class="kp">&amp;</span><span class="nc">for</span><span class="o">&lt;</span><span class="na">&#39;a</span><span class="o">&gt;</span><span class="w"> </span><span class="n">Foo</span><span class="o">&lt;&amp;</span><span class="na">&#39;a</span><span class="w"> </span><span class="kt">u8</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="na">&#39;a</span><span class="w"> </span><span class="kt">u8</span><span class="o">&gt;</span><span class="p">,</span><span class="w"></span>
<span class="p">)</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w">    </span><span class="kd">let</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">match</span><span class="w"> </span><span class="mi">22</span><span class="w"> </span><span class="p">{</span><span class="w"></span>
<span class="w">        </span><span class="mi">0</span><span class="w"> </span><span class="o">=&gt;</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"></span>
<span class="w">        </span><span class="n">_</span><span class="w"> </span><span class="o">=&gt;</span><span class="w"> </span><span class="n">y</span><span class="p">,</span><span class="w"></span>
<span class="w">    </span><span class="p">};</span><span class="w"></span>
<span class="p">}</span><span class="w"></span>
</pre></div>


<p>However, our "LUB" code (IIRC) is meant to enforce a strict equality check -- basically I don't know why this leak check would ever make something <strong>pass</strong> that did not before</p>



<a name="158997382"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158997382" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158997382">(Feb 20 2019 at 17:57)</a>:</h4>
<p>Seems surprising</p>



<a name="158997527"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158997527" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158997527">(Feb 20 2019 at 17:59)</a>:</h4>
<p>Although, looking in the git notes, I see :</p>
<div class="codehilite"><pre><span></span> This is needed for the universe-based code to handle
    `old-lub-glb-object`; that test used to work sort of by accident
    before with the old code.
</pre></div>


<p>from <a href="https://github.com/rust-lang/rust/commit/904a0bde93f0348f69914ee90b1f8b6e4e0d7cbc" target="_blank" title="https://github.com/rust-lang/rust/commit/904a0bde93f0348f69914ee90b1f8b6e4e0d7cbc">904a0bde93f0348f69914ee90b1f8b6e4e0d7cbc</a></p>



<a name="158997542"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158997542" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158997542">(Feb 20 2019 at 17:59)</a>:</h4>
<p>so <em>something</em> is going on there</p>



<a name="158997639"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/158997639" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#158997639">(Feb 20 2019 at 18:00)</a>:</h4>
<p>oh, I sort of maybe see how this change could make an error go away -- maybe we're getting an error more eagerly than we did before, we might apply the coercions rules better</p>



<a name="159010501"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159010501" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159010501">(Feb 20 2019 at 20:14)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> Do you feel comfortable backporting <a href="https://github.com/rust-lang/rust/pull/58056" target="_blank" title="https://github.com/rust-lang/rust/pull/58056">https://github.com/rust-lang/rust/pull/58056</a> and <a href="https://github.com/rust-lang/rust/pull/58592" target="_blank" title="https://github.com/rust-lang/rust/pull/58592">https://github.com/rust-lang/rust/pull/58592</a>? I've beta-nominated them and also nominated for the compiler team to approve tomorrow morning -- we might want to make sure they merge cleanly onto beta though</p>



<a name="159012691"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159012691" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159012691">(Feb 20 2019 at 20:40)</a>:</h4>
<p><span class="user-mention" data-user-id="116122">@simulacrum</span> I do -- they are in "seldom touched" parts of the code that haven't really changed since beta</p>



<a name="159012711"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159012711" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159012711">(Feb 20 2019 at 20:41)</a>:</h4>
<p>that said, I did want to maybe do a crater run on <a href="https://github.com/rust-lang/rust/issues/58592" target="_blank" title="https://github.com/rust-lang/rust/issues/58592">#58592</a> if we <em>can</em></p>



<a name="159012719"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159012719" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159012719">(Feb 20 2019 at 20:41)</a>:</h4>
<p>maybe we won't have time</p>



<a name="159012726"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159012726" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159012726">(Feb 20 2019 at 20:41)</a>:</h4>
<p>we can hopefully at least do a perf run</p>



<a name="159019353"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159019353" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159019353">(Feb 20 2019 at 22:02)</a>:</h4>
<p>I think we have time</p>



<a name="159019690"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159019690" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159019690">(Feb 20 2019 at 22:06)</a>:</h4>
<p>the try build should be ready soon</p>



<a name="159020123"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159020123" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159020123">(Feb 20 2019 at 22:13)</a>:</h4>
<p>right on <del>queue</del> cue</p>



<a name="159020135"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159020135" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159020135">(Feb 20 2019 at 22:13)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> <span class="user-mention" data-user-id="116122">@simulacrum</span> ^</p>



<a name="159020341"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159020341" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159020341">(Feb 20 2019 at 22:16)</a>:</h4>
<p>Started crater, perf runs</p>



<a name="159020343"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159020343" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159020343">(Feb 20 2019 at 22:16)</a>:</h4>
<p><span class="user-mention" data-user-id="116122">@simulacrum</span> thanks :)</p>



<a name="159082074"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159082074" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159082074">(Feb 21 2019 at 16:28)</a>:</h4>
<p>btw, <span class="user-mention" data-user-id="116010">@Aaron Turon</span>, I was thinking that maybe -- as a "next step" once we deal with the immediate leak-check thing -- we might try adding some constraints such that <code>'empty</code> is not permitted to result</p>



<a name="159088554"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088554" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088554">(Feb 21 2019 at 17:47)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> hm, ok. i'm feeling generally uneasy, in the sense that it feels hard to judge the implications of various choices. earlier i had convinced myself that <code>'empty</code> was totally fine to have around...</p>



<a name="159088659"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088659" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088659">(Feb 21 2019 at 17:48)</a>:</h4>
<p>I'd like to talk out the dropck implications too</p>



<a name="159088666"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088666" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088666">(Feb 21 2019 at 17:48)</a>:</h4>
<p>This is an "underspecified" area</p>



<a name="159088683"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088683" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088683">(Feb 21 2019 at 17:48)</a>:</h4>
<p>Anyway not a thing we need to immediately discuss</p>



<a name="159088707"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088707" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088707">(Feb 21 2019 at 17:49)</a>:</h4>
<p>I'm planning to r+ the PR as soon as I finish getting the stderr files blessed etc</p>



<a name="159088715"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088715" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Aaron Turon <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088715">(Feb 21 2019 at 17:49)</a>:</h4>
<p>OK, sounds good</p>



<a name="159088802"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088802" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088802">(Feb 21 2019 at 17:50)</a>:</h4>
<p>Then I will attempt the backport</p>



<a name="159088822"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159088822" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159088822">(Feb 21 2019 at 17:50)</a>:</h4>
<p>(which I expect to be fairly easy...)</p>



<a name="159089238"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159089238" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159089238">(Feb 21 2019 at 17:56)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span>  should we treeclose as well to make sure it goes through?</p>



<a name="159091168"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159091168" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159091168">(Feb 21 2019 at 18:23)</a>:</h4>
<p><span class="user-mention" data-user-id="126931">@centril</span> hmm good question! I don't really know. Maybe see if it lands naturally first? Does seem pretty imporatnt</p>



<a name="159091176"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159091176" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159091176">(Feb 21 2019 at 18:23)</a>:</h4>
<p>If we're trying to avert delaying the release, it feels like extreme machinations are justified</p>



<a name="159091229"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159091229" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159091229">(Feb 21 2019 at 18:24)</a>:</h4>
<p>I'd be happy if I saw a green travis mark first</p>



<a name="159091241"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159091241" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159091241">(Feb 21 2019 at 18:24)</a>:</h4>
<p>though locally it seems to be doing well</p>



<a name="159091242"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159091242" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159091242">(Feb 21 2019 at 18:24)</a>:</h4>
<p>definitely justified if we need to <span aria-label="slight smile" class="emoji emoji-1f642" role="img" title="slight smile">:slight_smile:</span></p>



<a name="159091244"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159091244" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159091244">(Feb 21 2019 at 18:24)</a>:</h4>
<p>I'm kind of happy to defer to release team on this point ;)</p>



<a name="159091276"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159091276" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159091276">(Feb 21 2019 at 18:25)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> cool; I'll see what happens with travis and decide ^^</p>



<a name="159093968"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159093968" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159093968">(Feb 21 2019 at 18:57)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> Delaying the release, beyond public perception, is essentially free (we'll have a few wrong dates in e.g. RELEASES.md but that doesn't really matter)</p>



<a name="159094015"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159094015" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159094015">(Feb 21 2019 at 18:57)</a>:</h4>
<p>I don't think there's any reason to treeclose -- we just need to make sure to retry as needed</p>



<a name="159094027"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159094027" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159094027">(Feb 21 2019 at 18:57)</a>:</h4>
<p><span class="user-mention" data-user-id="116122">@simulacrum</span> ok, yes. It's mostly public perception that I'm worried about. I think if it's on the scale of a few days etc it's fine. If we slip a release, or bump a week or something, that's a bigger deal</p>



<a name="159094132"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159094132" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159094132">(Feb 21 2019 at 18:58)</a>:</h4>
<p>So basically in terms of stopping the release you have until Thursday morning -- we can build artifacts etc and be ready to go</p>



<a name="159094172"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159094172" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159094172">(Feb 21 2019 at 18:58)</a>:</h4>
<p>We should have crater and some nightly baking by that point</p>



<a name="159094226"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159094226" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159094226">(Feb 21 2019 at 18:59)</a>:</h4>
<p>I think we'll be fine more or less</p>



<a name="159094302"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159094302" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159094302">(Feb 21 2019 at 19:00)</a>:</h4>
<p>Realistically our 6-week model means that if we delay a release by a week I'm honestly not _too_ concerned</p>



<a name="159094313"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159094313" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159094313">(Feb 21 2019 at 19:00)</a>:</h4>
<p>As I think <span class="user-mention" data-user-id="116010">@Aaron Turon</span> mentioned that seems a lot better then shipping potential known bugs</p>



<a name="159095145"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159095145" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159095145">(Feb 21 2019 at 19:10)</a>:</h4>
<p><span class="user-mention" data-user-id="116122">@simulacrum</span> the purpose of the tree-close is to avoid Niko or Aaron having to rebase and such... sure, we can retry all other PRs to make this one go first, but, treeclose seems cleaner and easier</p>



<a name="159095670"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159095670" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> simulacrum <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159095670">(Feb 21 2019 at 19:17)</a>:</h4>
<p>Sure, I meant that treeclose doesn't -- IIRC -- help with the retry bit and I presumed conflicts would be minimal anyway (i.e., we would emulate treeclose manually)</p>



<a name="159103462"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159103462" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159103462">(Feb 21 2019 at 20:55)</a>:</h4>
<p><span class="user-mention" data-user-id="126931">@centril</span> GG on being super quick with the retry :)</p>



<a name="159103488"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159103488" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159103488">(Feb 21 2019 at 20:55)</a>:</h4>
<p>=P</p>



<a name="159103651"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159103651" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159103651">(Feb 21 2019 at 20:57)</a>:</h4>
<p>I hope CI issues don't keep happening like they did with the previous PR</p>



<a name="159106071"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159106071" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159106071">(Feb 21 2019 at 21:29)</a>:</h4>
<p><span class="user-mention" data-user-id="126931">@centril</span> happened again :/</p>



<a name="159106077"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159106077" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159106077">(Feb 21 2019 at 21:29)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span>  CI is being real difficult <span aria-label="confused" class="emoji emoji-1f615" role="img" title="confused">:confused:</span></p>



<a name="159106221"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159106221" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159106221">(Feb 21 2019 at 21:30)</a>:</h4>
<p><span class="user-mention" data-user-id="126931">@centril</span> argh</p>



<a name="159106238"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159106238" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159106238">(Feb 21 2019 at 21:31)</a>:</h4>
<p>whats the command for treeclose?</p>



<a name="159106248"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159106248" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159106248">(Feb 21 2019 at 21:31)</a>:</h4>
<p><code>@bors treeclose=99</code>?</p>



<a name="159106645"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159106645" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159106645">(Feb 21 2019 at 21:36)</a>:</h4>
<p><span class="user-mention" data-user-id="116122">@simulacrum</span> probably knows</p>



<a name="159106870"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159106870" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159106870">(Feb 21 2019 at 21:39)</a>:</h4>
<p>(closed tree and did retry, pending again)</p>



<a name="159108976"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159108976" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159108976">(Feb 21 2019 at 22:07)</a>:</h4>
<p><span class="user-mention" data-user-id="126931">@centril</span> errors still look spurious, I Assume?</p>



<a name="159109057"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159109057" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159109057">(Feb 21 2019 at 22:08)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> ye, but its testing now, 32 min in</p>



<a name="159137707"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159137707" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> lqd <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159137707">(Feb 22 2019 at 07:41)</a>:</h4>
<p><a href="https://github.com/rust-lang/rust/issues/58592" target="_blank" title="https://github.com/rust-lang/rust/issues/58592">#58592</a> merged <span aria-label="tada" class="emoji emoji-1f389" role="img" title="tada">:tada:</span> and the crater run is <a href="https://crater-reports.s3.amazonaws.com/pr-58592/index.html" target="_blank" title="https://crater-reports.s3.amazonaws.com/pr-58592/index.html">done</a>: the 2 regressions it mentions don't seem related to the PR.</p>



<a name="159141991"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159141991" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159141991">(Feb 22 2019 at 09:22)</a>:</h4>
<p><span class="user-mention" data-user-id="116113">@lqd</span>  yep, both spurious <span aria-label="tada" class="emoji emoji-1f389" role="img" title="tada">:tada:</span></p>



<a name="159148251"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148251" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148251">(Feb 22 2019 at 11:09)</a>:</h4>
<p>I'm working on the beta backport now</p>



<a name="159148634"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148634" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148634">(Feb 22 2019 at 11:17)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span>  do we want to crater the backport or just r+ right away?</p>



<a name="159148686"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148686" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148686">(Feb 22 2019 at 11:18)</a>:</h4>
<p>Don't know</p>



<a name="159148693"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148693" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148693">(Feb 22 2019 at 11:18)</a>:</h4>
<p>One thing I wanted to check on was whether the new nightly (presuming it's issued) accrues any bug reports</p>



<a name="159148702"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148702" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148702">(Feb 22 2019 at 11:18)</a>:</h4>
<p>currently my beta backport is stalled at building LLVM :P</p>



<a name="159148708"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148708" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148708">(Feb 22 2019 at 11:19)</a>:</h4>
<p>but once that completes I expect to be able to put up a PR fairly easily</p>



<a name="159148826"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148826" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148826">(Feb 22 2019 at 11:20)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> neat; what date were we doing beta=&gt;stable promotion this time? crater took 2 days on nightly, so ideally we should have crater done on monday and be able to merge on the same day if you want to wait for crater</p>



<a name="159148911"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148911" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148911">(Feb 22 2019 at 11:22)</a>:</h4>
<p>Regarding date, I'm not entirely sure, but I think that <span class="user-mention" data-user-id="116122">@simulacrum</span> said something about Sunday night being a deadline for things to land</p>



<a name="159148916"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159148916" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159148916">(Feb 22 2019 at 11:22)</a>:</h4>
<p>There is also some flexibility here I think</p>



<a name="159149008"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159149008" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159149008">(Feb 22 2019 at 11:24)</a>:</h4>
<p><span class="user-mention" data-user-id="116009">@nikomatsakis</span> ok hmm... if you want to get it in by sunday we can still start crater and merge before; at least we'll get a report after</p>



<a name="159149033"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159149033" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159149033">(Feb 22 2019 at 11:25)</a>:</h4>
<p>we might get crater done before monday as well...</p>



<a name="159149107"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159149107" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> centril <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159149107">(Feb 22 2019 at 11:26)</a>:</h4>
<p>btw... the PR is still just beta-nominated... should we assume beta-accepted now as well?</p>



<a name="159149904"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159149904" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159149904">(Feb 22 2019 at 11:41)</a>:</h4>
<p>yeah, based on discussion in the compiler meeting I think so</p>



<a name="159149910"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159149910" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159149910">(Feb 22 2019 at 11:41)</a>:</h4>
<p>still working on backport, running some tests</p>



<a name="159149913"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159149913" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159149913">(Feb 22 2019 at 11:41)</a>:</h4>
<p>maybe 75% done</p>



<a name="159153643"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/144729-wg-traits/topic/reverting%20universes/near/159153643" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> nikomatsakis <a href="https://rust-lang.github.io/zulip_archive/stream/144729-wg-traits/topic/reverting.20universes.html#159153643">(Feb 22 2019 at 12:43)</a>:</h4>
<p>Backport PR: <a href="https://github.com/rust-lang/rust/pull/58641" target="_blank" title="https://github.com/rust-lang/rust/pull/58641">https://github.com/rust-lang/rust/pull/58641</a></p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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